Periodic Table Properties and Trends

Elements have different properties based on the valence electrons in their atoms.  These valence electrons and properties control how the atoms of that element will react with other elements.

Because the number and position of valence electrons an atom has matches up with its location on the Periodic Table, elements with similar valence electrons will have similar properties and are found in the same groups (up and down columns) on the Periodic Table.  In addition, as you go across each row from left to right and down each column on the Table, the elements show patterns in their properties and behaviors based on where they are located in the Table.

Several important properties of atoms we need to know about are:

1. Atomic Size (Radius)
2. Ionic Size (Radius)
3. Ionization Energy
4. Electronegativity

For each of these properties, you need to know what it means, what pattern it shows on the Periodic Table, and why it shows that pattern (what is going on inside the atom with the electrons to make that happen).  These following pictures and link to a flash animation will help with this understanding.

• Atomic Size (Radius) shown as a line graph.

• Atomic Size (Radius) shown as a bar graph in the Periodic Table.

• Click on this link to go to a Flash animation explaining about atomic properties, how they are related to electrons, and the patterns they show in the Periodic Table.

http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/atomic4.swf

• All of the properties and their patterns on the Periodic Table.

Electrons and PES

PES = Photo-Electron Spectroscopy is a special technique used to determine the location and number of electrons in an atom based on their energy.  It is another way of thinking about quantum numbers and it is experimental proof that electron configurations are accurate representations of the location and distribution of electrons within an atom.


Watch the following videos to get an idea of how the technique works and what the graphical results look like.  Then notice how we can use these graphs to get information about the electron configuration and identities of atoms.

• This second video has a worksheet that goes along with it that you will be asked to complete while watching the video.

• Lastly, read the diagram and text below AND the webpage shown in this link to help you understand what is going on with electrons in 3d and 4s, which orbtial they ACTUALLY fill in first, why they do it in that order, and why we learn electron configurations in the other order.

http://www.chemguide.co.uk/atoms/properties/3d4sproblem.html

Electron-electron repulsion

It takes 1312 kJ of energy to remove the electron from a mole of hydrogen atoms.  What might we expect this value to be for helium?  Helium contains two electrons, but its nucleus contains two protons; each electron "sees" both protons, so we might expect that the electrons of helium would be bound twice as strongly as the electron of hydrogen. The ionization energy of helium should therefore be twice 1312 kJ/mol, or 2612 kJ/mol. 

However, if one looks at the spectrum of helium, the continuum is seen to begin at a wavelength corresponding to an ionization energy of 2372 kJ/mol, or about 90% of the predicted value.

Why are the electrons in helium bound less tightly than the +2 nuclear charge would lead us to expect? 

The answer is that there is another effect to consider: the repulsion between the two electrons; the resulting electron-electron repulsion subtracts from the force holding the electron to the nucleus, reducing the local binding of each.

Electron-electron repulsion is a major factor in both the spectra and chemical behavior of the elements heavier than hydrogen. 

Unpaired Electrons: Paramagnetism and Diamagnetism

     Watch the two videos that follow to help you understand the difference between paramagnetism and diamagnetism, as well as how each phenomenon is caused by unpaired and paired electrons in atomic orbitals.  Also, check out the liquid oxygen in the second video!   (Total time = 10 minutes)

Electrons #5: Electrons in Atoms and Periodicity

Electron Configurations use quantum numbers (probability descriptions of where an electron is located outside of its nucleus) to differentiate among and list out all of the electrons in an atom.

• Watch this short video and then go to each of the website links that follow.  Pay extra attention to the discussion of Coulomb's Law and shielding.

• Answer the questions on each of the links.

http://www.sciencegeek.net/Chemistry/taters/Unit2ElectronNotations.htm

http://www.sciencegeek.net/Chemistry/taters/Unit3ValenceElectrons.htm

Electrons #4: Electronic Orbitals, Part II

Watch the following videos to learn about and help you understand the electronic structure of atoms. (Total time 30 minutes)

• 1st video goes into more detail about what the quantum numbers we use to describe where electrons are in each atom actually mean.

• 2nd video continues to discuss quantum numbers and uses more pictures of orbitals to help you understand how we have to talk about the electrons in an atom.

Electrons #3: Electronic Orbitals, Part I

Watch the following video to learn about and help you understand the electronic structure of atoms.

• 1st video has a good overview of the whole process.

• 2nd video explains the techniques and vocabulary chemists use to talk about electrons and their strange behavior as they move around the nucleus.

• Click on the following link to read about electron orbitals and electron configurations.

                         http://www.chemguide.co.uk/atoms/properties/atomorbs.html

• Look at the following two pictures.  The first is a simplified color-coded representation of the s, p, d, and f sublevels and the 1, 3, 5, and 7 orientations (orbtials) that each one has respectively.  The second picture shows some of the same orbitals as they really are, probability density plots of the electron's wave function.

Electrons #2: Electrons and Light

Click on this link and follow along with the Flash animation to help you understand how the quantum nature of electrons was discovered by looking at the colors of light produced when elements are heated.  The animation also connects the colors of light produced  to the location and behavior of electrons in an atom, relative to their nucleus.

http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/linesp16.swf